JP2006300942A - Method of controlling measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a measuring device, or particularly a method of operating especially a magnetic induction flow meter, and to obtain satisfactory SN ratio. <P>SOLUTION: A method of controlling the measuring device, in which measuring operation is clocked by a measuring frequency. The measured data, demanded in a measuring operation, is applied to a frequency analysis, and the measuring frequency is automatically controlled as a function of the frequency spectrum demanded by this. In this method, the satisfactory SN ratio is obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for controlling a measuring instrument having a measuring operation clocked at a measuring frequency.

  As an example using the above method, there is a measurement method of a magnetic induction flow meter. A magnetic induction flow meter is used to measure the flow rate of a medium flowing through a measurement tube and generates a magnetic field having a magnetic field element extending in a direction perpendicular to the longitudinal axis of the measurement tube by at least one field coil. And the voltage induced in the medium is detected via the two measuring electrodes. The underlying concept of the magnetic induction flowmeter goes back to 1832 Faraday, which proposed using the principle of electromagnetic induction for the measurement of flow velocity. According to Faraday's law for induction, a flowing medium that has a charge and passes through a magnetic field generates an electric field strength in a direction perpendicular to the flow direction and perpendicular to the magnetic field. The magnetic induction flowmeter generates a magnetic field having a magnetic field element extending in a direction perpendicular to the flow direction by a field coil. Within the magnetic field, the quantity element of the flow medium having a predetermined number of charges contributes to the electric field strength that occurs in the quantity element for the measured voltage detected by the electrodes.

  In a conventional magnetic induction flow meter, the measuring electrode is designed for either inductive or capacitive coupling with the flow medium. A prominent characteristic of a magnetic induction flow meter is the proportional relationship between the measured voltage and the velocity of the flow medium averaged over the cross section of the measuring note, in other words, the measured voltage and flow rate. .

  The measurement voltage detected at the measurement electrode as a function of flow rate is typically in the range of a few microvolts and a few millivolts. However, the noise voltage that interferes well overlaps the measured voltage. Typically, these noise voltages appear at different frequencies related to the ammeter supply power and pump stroke rate frequency. According to the impedance of the input circuit, the magnitude of the noise voltage can be increased to about several hundred mV.

  The object of the present invention is therefore to provide a method for operating a measuring instrument, in particular a magnetic induction flow meter, to obtain a good signal-to-noise ratio.

  With regard to the method described at the outset, the above mentioned objective is to automatically control the measurement frequency by subjecting the measurement variables detected during the measurement operation to a frequency analysis and in relation to the frequency defined thereby. Achieved by:

  Thus, according to the present invention, the measurement frequency for timing the measurement operation is not set in advance, but is controlled in relation to the detected noise frequency. There are various ways to control the measurement frequency.

  Basically, as implemented in the preferred embodiment of the present invention, the measurement frequency is controlled in such a way as to derive a measurement signal having the highest reachable signal to noise ratio. This is continuously controlled according to the noise size distribution, in other words, the interference spectrum, in a way that the measurement frequency can always extract the measurement signal with the highest possible signal-to-noise ratio. An important aspect here is that since the interference frequency is eliminated, the measurement frequency can be automatically and immediately shifted to a new interference spectrum, and the measurement frequency can be set to other values that lead to a better signal-to-noise ratio. There is an immediate response in the interference spectrum during measurement instrument control.

  In general, the interference spectrum includes several main frequencies that clearly rise from the noise level. Therefore, in a preferred embodiment of the invention, the measurement frequency is automatically controlled by at least one main frequency of the required spectrum. This can also be achieved in other ways. In particular, in the preferred embodiment of the invention, the measurement frequency is automatically controlled by one required main frequency, by an integral multiple of one main frequency, or by a fractional multiple of one main frequency.

  As an option, the preferred embodiment of the present invention provides that the measurement frequency is automatically controlled by a frequency different from the required main frequency. In another example of the invention, a predefined frequency range is selected for the measurement frequency, in which case the measurement frequency is pre-determined by some of the main frequencies required with maximum internal frequency separation. It is automatically controlled within the specified frequency range.

  In essence, it is possible to perform a frequency analysis regardless of the phase of the acquired vibration. However, in an embodiment of the invention, the frequency analysis is phase dependent. In this regard, a preferred example of the present invention is additionally to lock the phase with the phase of the acquired vibration having a frequency used to control the measurement frequency as described above, preferably in a phase dependent manner. Control the clocking mechanism of the measurement work.

  As mentioned above, the method according to the invention is particularly useful for the operation of magnetic induction flow meters. Accordingly, a preferred example of the invention is aimed at a measuring instrument in the form of a magnetic induction flow meter consisting of a measuring tube having a field coil and two electrodes. In this case, the field coil clocked at the measurement frequency is supplied with a coil drive current, the voltage is detected at the two measurement electrodes, and the voltage detected thereby is subjected to frequency analysis and the coil drive current. The measurement frequency that affects the field coil is controlled in relation to the required frequency spectrum. In particular, in the embodiment of the present invention, a constant current changing to the field coil is supplied.

  There are several ways in which the inventive method can be implemented and enhanced. On the other hand, attention should be paid to the following detailed description of the dependent claims and embodiments of the present invention with reference to the accompanying drawings.

  Embodiments of the present invention will be described below.

  The magnetic induction flow meter shown in FIG. 1 comprises a measuring tube 1 having two electrodes that detect the voltage induced by the medium flowing therethrough. The required magnetic field is generated by the two field coils 3.

The field current generator 4 supplies a coil drive current to the field coil 3. The microcontroller 5 operates the field current generator 4 and the field coil 3 clocked at a preselected measurement frequency is supplied with a changing constant current. The measurement frequency at which the magnetic induction flow meter n measurement operation is clocked is selected in the manner described below:
The voltage induced in the flow medium by the magnetic field is detected by the measurement electrode, supplied to the preamplifier 6, and sent from there to the A / D converter 7. However, in addition to the voltage induced in the medium, the noise voltage is similarly combined and sent to the microcontroller 5 via the preamplifier 6 and the A / D converter 7 in the same way as the induced voltage. The value obtained in this way is stored in a memory module 8 connected to the microcontroller 5, and the measurement data required in the measurement operation is controlled under the control of the microcontroller 5, in this case a fast Fourier transform (FFT). ) Is subjected to frequency analysis. This results in a frequency spectrum and an interference spectrum 10 consisting of a valid information signal 9 output via a separate output.

  The interference spectrum 10 is again optimized for the microcontroller 5 and used to control the measurement frequency. In the embodiment described above, the measurement frequency is automatically controlled at one of the main frequencies of the interference spectrum, preferably a superior interference frequency. In this case, the frequency analysis is performed in a phase-dependent manner in which the phase of the oscillation providing the main frequency is phase-locked by the phase-dependent time of the measurement operation, in particular by the method in which the measurement frequency is controlled.

  As a result, a magnetic induction flow meter can be obtained that provides a very good signal-to-noise ratio without the occurrence of significant interference due to parasitic noise voltages.

FIG. 1 is a block diagram of a magnetic induction flow meter played by the method of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Measurement tube 2 Measurement electrode 3 Field coil 4 Field current generator 5 Microcontroller 6 Preamplifier 7 A / D converter 8 Memory module 9 Information signal 10 Interference spectrum

Claims (10)

In the control method of the measuring device in which the measurement work is clocked at the measurement frequency,
The measurement data required for the measurement operation is subjected to frequency analysis, and the measurement frequency is automatically controlled in relation to the frequency spectrum defined by the frequency analysis.   The method according to claim 1, wherein the measurement frequency is automatically selected in a method for obtaining a measurement signal having the highest S / N ratio.   The method according to claim 1, wherein the measurement frequency is controlled in association with at least one main frequency from a defined frequency spectrum.   The measurement frequency is automatically controlled at the at least one main frequency, an integer multiple of the at least one main frequency, or a fractional multiple of the at least one main frequency. The control method of the measuring apparatus according to claim 3.   The method according to claim 3, wherein the measurement frequency is automatically controlled at a frequency other than the at least one main frequency.   A predefined frequency range is allocated to the measurement frequency, and the measurement frequency is automatically controlled within the predefined frequency range by several required main frequencies, with a maximum total frequency separation. The method of controlling a measuring apparatus according to claim 3.   The method for controlling a measuring apparatus according to claim 1, wherein the frequency analysis is performed in a phase discrimination method.   8. The method of controlling a measuring apparatus according to claim 7, wherein the measuring operation is preferably controlled by a phase-dependent method in which the phase is fixed at a specific phase.   The measuring instrument is a magnetic induction flowmeter including a field coil and two measuring electrodes, and a measuring tube clocked at a measuring frequency, and the field coil is supplied with a coil driving current, The voltage is detected by two measurement electrodes, the detected voltage is subjected to frequency analysis, and the measurement frequency when the coil drive current is supplied to the field coil is controlled as a function of a predetermined frequency spectrum. The method for controlling a measuring apparatus according to any one of claims 1 to 6.   The method for controlling a measuring apparatus according to claim 9, wherein a constant current that changes is supplied to the field coil.

Images